Hi,
I have looked at this in more detail. I found this thread:
http://zookeeper-user.578899.n2.nabble.com/Create-nested-paths-td7331156.html
which said: "Sample usage can be found in
org.apache.zookeeper.test.MultiTransactionTest"
Using part of that code to illustrate. What I would like to be able to
do is something akin to:
Integer REF1;
Integer REF2;
Integer REF3;
zk.multi(Arrays.asList(
/* Create */
REF1 = Op.create("/multi", null, new byte[0],
Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT_SEQUENTIAL),
Op.setData("", REF1, "DATA_VALUE".getBytes(), 0),
REF2 = Op.create("/a", REF1, new byte[0],
Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT),
REF3 = Op.create("/1", REF2 new byte[0],
Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT),
Obviously, use of Integer is just for illustration and the CAPs are for
effect. However, with this type of API the "multi" implementation
could, for a single input list, maintain a structure of previous Op's
that could then be referred to in future ops. When a "reference" was
passed in that was non-null, it would just that reference in some
intelligent way. Above, the use of REF1 on the "setData" method would
lookup the path created for REF1 and use that to set the data. The use
of REF1 in the Op.create would APPEND the input path to the path created
for REF1. Thus, the REF2 line might create a path like /multi_00000001/a
Ideally, I would like to be able to replace the "0" in various "setData"
calls, not sure how to do that exactly, but the above would be a decent
start. [If a node already existed and I was calling the Op.setData
method and wanted to follow that with a Op.check call, I believe that I
currently have no way of knowing the version number....]
Does this make more sense than the gibberish I was trying below?
thanks,
Joe
On 5/16/2012 8:06 PM, Joe Gamache wrote:
No thought about two znodes being synchronized at all.
The higher level intent of the first (code) example is: how do you get
the version number for a set operation and use that value in the set
atomically? For the second one it is: how to I create and lock a
znode atomically? [maybe the Lock znode is attached to the node I am
creating, maybe in another structure? I don't really care, just can I
do it atomically?]
Another way to do what I would like would be to create a znode
structure that is not "attached" to the existing one at all, then once
I have it the way it should be, attach it to an existing node.
However, I am quite certain this is not possible....
On 5/16/2012 7:21 PM, Ted Dunning wrote:
It looks like you are assuming that the versions of two znodes are
synchronized. That seems pretty dangerous.
What is the higher level intent here? Would it better to simply
build a multi to update both znodes?
Sent from my iPhone
On May 16, 2012, at 11:59 AM, Joe Gamache<[email protected]>
wrote:
I need to do something like the following:
Stat stats = nodeToSet.getStat();
if (stats != null) {
int version = stats.getVersion();
stats = client.getZk().setData(path, data, version);
(data was preset in code not shown). Since I have multiple
processes all vying to do things, in the worst case (which happens
too frequently), two processes execute the above at basically the
same time, which causes errors. I thought I might be able to use
Multi to do this atomically, but I cannot figure out how to use the
result (the version number above) from one Op in a later Op. Is
this possible?
This was the simplest example I could find, but this happens often -
usually with Paths. For instance, sometimes I create a zookeeper
node and want a "LOCK" node underneath it. If I follow the "recipe"
and use an ephemeral sequential node as the lock, how can I refer to
sequence in a Path in subsequent Op added to a "multi" or is there
any way to do it atomically? Sorry that was so very wordy. What I
was really trying to ask, is how do I create and lock a node
atomically?
thanks for any help, insight!
joe
